Various copolymers that contain cyclic structures in a main chain have been known. For example, Non-Patent Literature 1 discloses an ethylene-cyclopentene random copolymer which has, as a monomer unit, a structure in which a 1,2-substituted cyclopentane cyclic structure and an alkyl chain are bonded alternately. Further, Patent Literature 1 discloses a copolymer of (i) ethylene and/or α-olefin having 3 to 20 carbon atoms in a carbon chain, and (ii) substituted cyclohexene and/or unsubstituted cyclohexene.